Respiratory Monitoring Devices & Reporting for SpO2, SvO2 & ETCO2

Instructor: Alexandra Unfried

Alexandra earned her master's degree in nursing education and is currently a hospital supervisor/administrator.

There are a variety of devices used for monitoring and reporting respiratory status using SpO2, SvO2, and ETO2. This lesson will discuss pulse oximetry, SvO2 monitoring, and capnography.

Respiratory Monitoring

Carl is a nurse on the intermediate care unit (IMC). His unit specializes in respiratory diseases and he is taking care of three patients. Each of his patients has a different type of respiratory condition and monitoring device. He begins his shift by assessing each of his patients.

Pulse Oximetry

Carl's first patient has resolving pneumonia and is being monitored for their oxygen level using a non-invasive pulse oximeter. Carl assesses the patient and makes sure that the monitoring device is set up properly while he explains what he is doing to the patient.

Pulse oximetry monitors the oxygen saturation (SpO2) in the body by measuring the oxygen in the hemoglobin. A sensor with a two-light photodetector is used to detect light that is absorbed by oxygenated and deoxygenated hemoglobin. The sensor should be placed on an area with good blood flow. There are two types of pulse oximetry sensors.

  • Wrap around sticker sensor: can be placed on the fingers, thumb, nose, or big toe
  • Clip sensor: can be placed on the finger or earlobe

Clip sensor for pulse oximetry
Clip sensor for pulse oximetry

Carl sees that his patient has a wrap sensor on his right index finger. He knows that he needs to check the sensor at least every eight hours to make sure it is working correctly. A clip sensor is checked every four hours.

Carl assesses the right index finger looking for:

  • Good circulation
  • Warm temperature
  • Absence of swelling

Carl also knows that any change in his patient's level of consciousness may indicate a decreased oxygen saturation level, which requires an arterial blood gas test since pulse oximetry is not a diagnostic device. The patient's oxygen saturation is currently 98%, so Carl documents that in the chart along with what type of oxygen the patient is receiving and the patient's temperature.

Mixed Venous Oxygen Saturation

Carl moves onto his next patient who has congestive heart failure. This patient is more critical than his last patient, and is on a venti-mask for oxygen and has a pulmonary artery catheter (PAC) to monitor their respiratory status. The PAC is able to monitor the mixed venous oxygen saturation (SvO2). The SvO2 tells Carl the end result of oxygen use and delivery by measuring the oxygen from blood in the pulmonary artery. This means that it shows how well oxygen is reaching outlying tissues by using estimates and trends.

Carl's patient has a SvO2 of 70% which is normal. The PAC is monitoring trends which show how well interventions are working to improve the patient's respiratory status. Interventions include receiving fluid or inotropes, changes in medications (vasodilators), and dialysis.

It has been a while since Carl took care of patient with SvO2 monitoring. He reviews how it is interpreted so he knows what to do with his results.

Increased SvO2

  • Indicates increased oxygen delivery seen with an increased FiO2 (inhaled oxygen), hyperoxia (tissues are receiving too much oxygen), or during hyperbaric oxygen treatment
  • Seen with decreased oxygen demand indicating hypothermia, anesthesia, or a neuromuscular block
  • Hyperthyroidism, septic shock, or liver disease may be present in high flow states

Decreased SVO2

  • Indicates decreased oxygen delivery seen with decreased hemoglobin (due to anemia, bleeding, or dilution), decreased oxygen saturation (hypoxemia), or a decreased Q waveform of the heart rhythm
  • Seen with an increased demand of oxygen, which is indicative of increased temperature, pain, uncontrollable shaking, or seizures

Carl will continue to monitor the SvO2 in his patient and will report any change in the result. Now that he has reviewed how to interpret the SvO2, he will know what to report to the doctor, and can provide early intervention for the patient if needed.


Carl moves onto his third patient to complete an assessment. This patient just returned from the post anesthesia care unit (PACU) after having back surgery. Since the patient was under anesthesia, they are being monitored with a capnography machine. Capnography assesses ventilation which is shown as a number and a graph on the display screen. The waveform shows the level of carbon dioxide in the exhaled air, also known as end tidal CO2 (ETCO2). Carl is glad to see that the machine is hooked up properly to the patient's nasal prongs. The measurements are useful in diagnosing and monitoring respiratory distress.

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